Artificial intervertebral disc spacers

ABSTRACT

Intervertebral disc spacer components include spherical articulating surfaces to promote more natural spinal movement between one or both vertebrae. The invention broadly encompasses the provision of a single artificial disc replacement end plate (ADR EP) with a bi-convex disc spacer where the maximum vertical distance of the spacer is centrally located or a disc spacer with two or more components, wherein where at least one of the articulations between spacer components is spherical (a generally convex articulating surface mated with a generally concave articulating surface). The invention may further include the step of shaping the vertebral endplates to improve the articulation between the disc spacer and the vertebra by increasing the surface contact between the disc spacer and the vertebra. Although described in terms of artificial disc replacements, the apparatus and methods are applicable to other areas of the body, including knee replacements.

REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Provisional PatentApplication Serial No. 60/375,212, filed Apr. 24, 2002, the entirecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally spine surgery and, inparticular, to artificial intervertebral disc spacers.

BACKGROUND OF THE INVENTION

[0003] Spacers, usually constructed of metal, have been used to treatunicompartmental arthritis of the knee. In such cases, a knee prosthesisis placed in the arthritic joint spacer. The surfaces of the spacer areshaped to articulate with the femoral condyle and the tibia plateau.

[0004] Intervertebral prosthetic discs are also known. One example ispresented in U.S. Pat. No. 5,888,226, which teaches the use of discspacers with convex vertebral surfaces, where the maximum verticaldimension is non-central. This reference also teaches the use of flatarticulating surfaces between disc spacer components. Another example isgiven in U.S. Pat. No. 4,348,921, which discloses the use of a one- ortwo-piece disc spacer. The two-component disc spacer may articulatethrough a spherical joint.

[0005] The device described in the '921 patent is designed to avoidmovement between the disc spacer and the vertebrae. The disclosuredescribes corrugations or projections to improve the “friction fit”. Aflange is includes that would further inhibit movement between the discspacer and the vertebrae, and the specification mentions that it isimportant that the prosthesis does not allow lateral movement.

[0006]FIG. 1 is a lateral view of the spine and a prior-art artificialdisc replacement (ADR) spacer. FIG. 2 is a view of the lateral aspect ofthe spine and another prior-art disc spacer which is textured to inhibitmotion between the spacer and the vertebrae. Based upon such approaches,the need remains for disc spacer component device that permits morenatural spinal movement.

SUMMARY OF THE INVENTION

[0007] This invention improves upon the prior art by providing discspacer components including spherical articulating surfaces to promotemore natural spinal movement. Depending upon the embodiment, sphericalarticulations may be permitted between one or both vertebrae. Sucharticulations may occur between the vertebrae and two pairs of sphericalarticulating surfaces between the disc spacer components, or between thevertebrae and one pair of spherical articulating surfaces between thedisc spacer components.

[0008] The invention broadly encompasses the provision of a singleartificial disc replacement end plate (ADR EP) with a bi-convex discspacer where the maximum vertical distance of the spacer is centrallylocated or a disc spacer with two or more components, wherein where atleast one of the articulations between spacer components is spherical (agenerally convex articulating surface mated with a generally concavearticulating surface).

[0009] Components according to the invention may be composed of anybiologically acceptable material including chrome cobalt, titanium,polyethylene, Nitinol, ceramic, stainless steel, and polymers, includingelastomers. At least one component may have elastic or spring-likeproperties.

[0010] The invention may further include the step of shaping thevertebral endplates to improve the articulation between the disc spacerand the vertebra by increasing the surface contact between the discspacer and the vertebra. Although described in terms of artificial discreplacements, the apparatus and methods are applicable to other areas ofthe body, including knee replacements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a lateral view of the spine and a prior art disc spacerADR;

[0012]FIG. 2 is a view of the lateral aspect of the spine and anotherprior art disc spacer;

[0013]FIG. 3A is a lateral view of the disc spacer of the presentinvention;

[0014]FIG. 3B is a lateral view of the embodiment of the device shown inFIG. 3A;

[0015]FIG. 4A is a view of the top of the disc spacer shown in FIG. 3A;

[0016]FIG. 4B is a view of the top of an alternative shape of the discspacer shown in FIG. 4A;

[0017]FIG. 5A is a sagittal cross section of the disc spacer shown inFIG. 3A;

[0018]FIG. 5B is a view of the top of the central component in theembodiment of the device shown in FIG. 5A;

[0019]FIG. 5C is a view of the top of an alternative central componentto that shown in FIG. 5B;

[0020]FIG. 5D is a view of the top of an alternative central componentto that shown in FIG. 5C;

[0021]FIG. 5E is a view of the lateral aspect of the spine and theembodiment of the device shown in FIG. 5;

[0022]FIG. 5F illustrates how depressions may be used in lieu of athrough-hole;

[0023]FIG. 6A is a lateral view of an alternative embodiment of the discspacer;

[0024]FIG. 6B is a lateral view of the embodiment of the spacer shown inFIG. 6A;

[0025]FIG. 7 is a sagittal cross section of the embodiment of the deviceshown in FIG. 6A;

[0026]FIG. 8A is a view of the lateral aspect of an alternativeembodiment of the disc spacer;

[0027]FIG. 8B is a sagittal cross section of the embodiment of the discspacer shown in FIG. 8A;

[0028]FIG. 9A is a sagittal cross section of an alternative embodimentof the device;

[0029]FIG. 9B is a lateral view of the embodiment of the disc spacershown in FIG. 9A;

[0030]FIG. 9C is a lateral view of an alternative embodiment of thedevice shown in FIG. 9B;

[0031]FIG. 9D is a lateral view of a flexed spine and the embodiment ofthe device shown in FIG. 9C;

[0032]FIG. 10A is sagittal cross section of the spine and an alternativeembodiment of the device;

[0033]FIG. 10B is a sagittal cross section of the spine and analternative embodiment of the device shown in FIG. 10A;

[0034]FIG. 11 is a sagittal cross section of the spine and analternative embodiment of the disc spacer;

[0035]FIG. 12 is a sagittal cross section of an alternative embodimentof the device drawn in FIG. 9A;

[0036]FIG. 13 is a sagittal cross section of an alternative embodimentof the device shown in FIG. 5A;

[0037]FIG. 14 is a sagittal cross section of an alternative embodimentof the device shown in FIG. 13; and

[0038]FIG. 15 is sagittal cross section of the knee and an example of anembodiment of the device designed for use in the knee.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention is a spacer that can be placed into thedisc space. The spacer is not fixed to either vertebra. Rather, theprosthesis is free to self-center with spinal movement. The spacer alsoprovides at least a certain degree of distraction. The prosthesis can bemade of metal, a polymer such as polyethylene, or ceramic, or anycombination thereof, such as metal/polyethylene, metal/ceramic,ceramic/polyethylene, and so forth. The articulated spacers disclosedherein may also be used in the knee.

[0040] Shape memory properties of the material may be helpful. Thespacer is generally bioconvex in shape to closely match the concavitiesof the vertebrae.

[0041] Reference is again made to the drawings, wherein FIG. 3A providesa lateral view of a disc spacer according to the invention includingthree components, namely two outer convex components 302, 304, and acenter component 310. The surfaces of the outer, convex, components 302,304 are polished to facilitate articulation with the vertebrae and thecenter component 310. FIG. 3B is a lateral view of the embodiment of thedevice drawn in FIG. 3A, with the outer components 302, 304 seen in aforward-most position. Movement between these disc spacer componentsfacilitates more natural spinal motion.

[0042]FIG. 4A is a view of the top of the disc spacer drawn in FIG. 3A.FIG. 4B is a view of the top of an alternative shape of the disc spacerdrawn in FIG. 4A. FIG. 5A is a sagittal cross section of the disc spacerdrawn in FIG. 3A, perhaps better illustrating how the disc spacerarticulates with the vertebrae above and below the disc spacer. The discspacer components also articulate through generally convex and concavearticulating surfaces above and below the central disc spacer component.Thus, the disc spacer articulates through four different locations.Projections 502, 504 from the outer components fit within a hole 504 inthe inner, central, component. As shown in FIG. 5E, depressions 550 maybe used in lieu of a through-hole.

[0043] In all cases cooperation between the components preventsdissociation of the spacer. The outer components could reversiblyflatten in response to axial loads. The outer components could haveelastic properties much like the components described in my co-pendingU.S. patent application Ser. No. 60/399,876, incorporated herein byreference.

[0044]FIG. 5B is a view of the top of the central component in theembodiment of the device drawn in FIG. 5A. FIG. 5C is a view of the topof an alternative central component to that drawn in FIG. 5B, whereinthe central opening is oval. FIG. 5D is a view of the top of analternative central component to that drawn in FIG. 5C, wherein thecomponent is oval.

[0045]FIG. 5E is a view of the lateral aspect of the spine and theembodiment of the device drawn in FIG. 5A. Note that movement betweenthe disc spacer and the vertebrae allows the disc spacer to“self-center.” For example, the disc spacer may move forward duringspinal extension. Movement also occurs through the two articulationsbetween the three disc spacer components.

[0046]FIG. 6A is a lateral view of an alternative embodiment of the discspacer. The disc spacer has three components. FIG. 6B is a lateral viewof the embodiment of the spacer drawn in FIG. 6A. The outer componentsare drawn in a tilted position. Tilting of the outer componentsfacilitates spinal motion.

[0047]FIG. 7 is a sagittal cross section of the embodiment of the devicedrawn in FIG. 6A. The disc spacer articulates with the vertebra aboveand below the spacer. The outer disc spacer components also articulatewith the central, bi-concave, disc spacer component. As described inconjunction with FIG. 4, the disc spacer may be circular or oval.

[0048]FIG. 8A is a view of the lateral aspect of an alternativeembodiment of a disc spacer incorporating two components. FIG. 8B is asagittal cross section of the embodiment of the disc spacer drawn inFIG. 8A. Both components articulate with the vertebra above and belowthe disc spacer. The spacer components also articulate with each otherthrough generally convex and generally concave articulating surfaces. Alocking projection similar to that shown in FIG. 5A, is used to preventthe components from dissociating.

[0049]FIG. 9A is a sagittal cross section of an alternative embodimentof the device. The spacer has two components. Both components articulatewith each other and the vertebrae. FIG. 9B is a lateral view of theembodiment of the disc spacer drawn in FIG. 9A. FIG. 9C is a lateralview of an alternative embodiment of the device drawn in FIG. 9B. Thecomponents are shaped to increase the motion across the articulationbetween the disc spacer components. FIG. 9D is a lateral view of aflexed spine and the embodiment of the device drawn in FIG. 9C.

[0050]FIG. 10A is sagittal cross section of the spine and an alternativeembodiment of the device. Articulating components similar to those drawnin FIG. 8B articulate with a single ADR endplate. The ADR endplate (EP)is press fit or otherwise connected to the vertebra. Preferably, the ADREP does not move relative to the vertebra (EP). FIG. 10B is a sagittalcross section of the spine and an alternative embodiment of the devicedrawn in FIG. 10A. The inferior articulating component is connected tothe vertebra much like an ADR EP is connected to the spine. Articulationis limited to the two disc spacer components and the superior componentand the vertebra superior to the disc spacer. As illustrated in thefigure, the disc spacer may articulate with only a portion of thevertebral EP.

[0051]FIG. 11 is a sagittal cross section of the spine and analternative embodiment of the disc spacer. The inferior component of thedisc spacer drawn in FIG. 9A is attached to the vertebra below the discspacer. FIG. 12 is a sagittal cross section of an alternative embodimentof the device drawn in FIG. 9A. The inferior surface of the inferiordisc spacer component is flat. The flat surface of the disc spacercomponent facilitates translation of the vertebrae.

[0052]FIG. 13 is a sagittal cross section of an alternative embodimentof the device drawn in FIG. 5A. The vertebral surfaces of both discspacer components are flat. The vertebral EPs could be shaped to improvethe surface contact between the disc spacer and the vertebrae. FIG. 14is a sagittal cross section of an alternative embodiment of the devicedrawn in FIG. 13. The articulating surfaces on one side of the centralcomponent are flat. The flat articulating surfaces facilitatetranslation.

[0053]FIG. 15 is sagittal cross section of the knee and an example of anembodiment of the device designed for use in the knee. The two componentdevice articulates with the tibia and the femur. The two components alsoarticulate with each other. All of the articulating surfaces are highlypolished. Alternatively, the surfaces of the spacer components thatarticulate with the bones of the knee could be less polished toencourage movement between the spacer components rather than movementbetween the spacer and the bones. In particular, it may be beneficial todiscourage movement between the spacer and the tibia. The spacer may becoupled with a device described in my co-pending U.S. patent applicationSer. No. 60/376,505, incorporated herein by reference. The devicestaught in this other application also prevent extrusion of articulatingdevices from the joints of the body.

I claim:
 1. A disc spacer, comprising: a device that articulates withrespect to: a) at least one spherical interface involving convex andconcave surfaces, and b) at least one vertebral endplate.